"@Clooney:
Thank you for looking at the GPS fix problem!
In mavlink.ino, line 290 should be changed too."

"Thank you all for the great work here!
I'm using a modified version of Clooneys implementation and now it runs very smooth.

But before I had to fight with a little bug:
The Teensy sends GPS Data only if the APM signals a 3D fix to avoid the use of…"